Manufacture of rubber latex-deposited articles



J. S- RUMBOLD MANUFACTURE OF RUBBER LATEX-DEPOSITED ARTICLES Dec. 13, 1955 Filed Oct 22, 1952 ATTORNEY 1 2,726,924 MANUFACTURE OF RUBBER LATEX-DEPOSITED ARTICLES John S. Rumbold, Woodbridge, Conn., assignor to United States Rubber Co., New York, N. Y., a corporation of New Jersey Application October 22, 1952, Serial No. 316,129 8 Claims. (CI. 18-48) This invention relates to the manufacture of rubber latex-deposited articles having integrally reinforced openings.

It is known to integrally reinforce the openings of rubber latex articles by providing deposition or dipping forms for rubber latex articles with metal ribs having sharp edges protruding from the deposition surface whereby a thickened latex deposit is built up in the angles between the sides of the protruding ribs and the deposition surface, and whereby the latex deposits more thinly over the sharp edges than over the main deposition surface of the form. t is also known that latex will deposit more thinly over the sharp edge formed at the intersection of two surfaces of a deposition form which meet at an angle of say 90 degrees or less, than over the surfaces of the form extending on both sides of the sharp edge. With very thin rubber articles, it has been suggested that the dried deposit may be severed by tearing at the sharp edge. This leaves a jagged run at the opening of the article, and is not practicable for articles of a thickness suitable for shoes and similar products. It has been suggested that the rubber deposit on the surface of the form having protruding metal ribs with sharp edges may be cut at the sharp edges by pressing a roller against the sharp edges leaving integral reinforcing beads at the cut edge of the article. When a roller or other pressure instrument is used, it is almost impossible to avoid damaging both latex and knife edge when the latex is soft and wet. On the other hand, when the latex is completely dry, it becomes so strong that considerable pressure must be exerted to force the knife through it, and the edge soon becomes blunted, and in regular use more and more difficulty is encountered in cutting the film.

I have found that the above disadvantages can be overcome and the rubber deposited from latex on a sharp edge on a deposition form can readily be severed Without damage to the sharp edge by merely applying a rubber swelling agent to the deposit on the edge, as by pressing against it with a soft pad moistened with the swelling agent.

In the drawings:

Fig. 1 is a side elevation of one type of a shoe dipping form having a protruding rib with a sharp edge on which the present invention may be practiced;

Fig. 2 is a cross sectional enlarged view of a portion of the form of Pig. 1 in the vicinity of the protruding rib with rubber deposited from latex thereon; and

Fig. 3 is a cross sectional elevation of another type of shoe dipping form with a sharp edge formed at the intersection of two surfaces of the form meeting at substantially right angles at the top of the form with rubber deposited from latex thereon and on which the present invention may be practiced.

Referring more particularly to Figs l and 2 of the drawing, the metal shoe dipping form has a circumferential protruding metal rib 11 integral therewith or attached thereto at the desired height for the shoe opening, and somewhat below the top 12 of the form. The rib 11 is provided with a sharp edge 13. A rubber deposit is built up on the form by conventional dipping procedure, generally by one or more dippings in latex and coagulant above the rib 11 and below the top 12 asshown at 14 in Fig. 2, preferably with the form being reversed after a latex or coagulant dip to allow the latex or coagulant to run down from the body of the form to the rib 11 in order to assure a thickened deposit in the angle between the side of the rib and the surface of the form. The latex coagulum will be deposited as shown in Fig. 2 with thickened bead-forming deposits 15 and 16 in the angles between the sides 17 and 18 and the portions 19 and 20 of the dipping surface of the form above and below the rib 11, and with a thinner deposit 21 over the sharp edge 13 than the regular deposits 22 and 23 on the surface of the form above and below the thickened deposits 15 and 16. After the desired thickness of coagulum deposit has been built up on the main surface of the form, the deposit is dried in order to give it sulficient strength to avoid bruising or other damage in applying the rubber swelling agent to the deposit over the sharp edge. As a measure or guide, the latex deposit should be dried sulfciently so that shrinkage places the rubber film under tension over the sharp edge 13 of the rib 12. The thus dried deposit is severed at the sharp edge 13 by treating the deposit on the sharp edge with a rubber swelling agent. I have been able to successfully sever natural rubber latex deposits with gasoline at the knife edge by the method of the present invention when the freshly coagulated deposit had been dried for 10 and 20 minutes at room temperature to a moisture content of 32% and 31% by weight, and more readily when the coagulum deposit had been dried for one hour at F. to a moisture content of 5% by weight, the less moisture there was in the film, the easier it was to sever at the sharp edge with the rubber swelling agent. Further drying is not detrimental, but it is preferred that it not be accompanied by too great a degree of vulcanization since the rubber swelling agent takes longer to sever fully cured films than uncured or partially cured films. Generally, the combined sulfur content of the film at the time of severing by application of the rubber swelling agent should not be over 0.5% by weight of the rubber. The rubber swelling agent may be applied by pressing against the sharp edge with a soft pad impregnated with the swelling agent, or the form may be dipped in a rubber swelling agent and quickly removed. The rubber deposit severs immediately at the sharp edge 13. Similarly, the rubber deposit may be severed at the sharp edge formed by the intersection of two surfaces of a form which meet at right angles as in the form of Fig. 3. As

shown in Fig. 3, the shoe form 30 having a main deposition surface 31, is the correct height for the shoe so that the form is dipped above the top 32 of the form in forming the rubber deposit. In the figure, the form is inverted from its dipping position. The rubber coagulum deposit will be of the desired thickness at 33 over the main surface of the form. The top surface 32 intersects the main surface 31 at a sharp edge 34 around the top of the form. The rubber coagulum deposit will be thinner at 35 on the sharp edge 34 than on the main surface of the form at 33, and thicker on each side of the sharp edge 34, as at 36 and 37, than at 33. The rubber deposit may be severed at the sharp edge 34 by application of a rubber swelling agent, as described above with reference to the deposit over the sharp edge 13 of the form shown in Figs. 1 and 2.

The present preferred rubber swelling agent for severing the latex rubber film on the sharp edge of the form is gasoline. If desired, the rubber swelling agent may have rubber dissolved in it as in the form of a rubber cement. Any of the well-known rubber swelling agents may be used, c. g., aliphatic hydrocarbon oils; petroleum products such as gasoline, kerosene, and light fuel oils of the paraffin series; aromatic hydrocarbons such as benzene and toluene; coal tar fractions such as xylene and solvent naphtha; turpentine; and chlorinated hydrocarbons such as carbon tetrachloride and ethylene dichloride, and many others. For various rubber swelling agents, see Science of Rubber by Memmler, published by Reinhold Book Company, N. Y., 1934, pages 472 to 481, on Swelling and Solution of Rubber, and Chemistry and Technology of Rubber by Davis and Blake, published by Reinhold Publishing coiporation, N. Y., 1937, pages 181 to 194, on Structure and Behavior of Rubber in Solvents. Generally, rubber swelling agents having a boiling range between 60 C. and 280 C. are preferred. If the forms are at an elevated temperature up to about 80 C. from drying of the latex deposit, swelling agents having a boiling range near the upper limit noted above are satisfactory, whereas if the forms are cool at the time of treatment of the rubber deposit with the swelling agents, swelling agents having a boiling range nearer the lower limit noted above are preferred.

As an illustration of the practice of the invention, the form is dipped into a latex coagulant such as a 10% (by weight) ethanol solution of calcium nitrate to above the rib 11, and the form is removed from the coagulant solution and inverted, allowing some of the coagulant solution to collect on the edge 13'of the rib 11 and in the angle between the edge 13 and the surface 20 of the form below the rib 11. The form is then dipped in a conventionally compounded natural rubber latex containing vulcanizing ingredients to above the rib 11 as at 14, and allowed to remain in the latex until the desired thickness of film has been built up on the surface of the dipping form as at 28. The form is then removed, dipped again in the coagulant to set the latex film, removed and dipped in water to wash the fresh coagulum. After washing, the deposit is dried sufficiently so that it is under tension over the sharp edge 13 of the rib 11. Generally the deposit will be dried to less than 20% by weight moisture content. A cotton pad impregnated with gasoline is pressed against the rubber deposit on the sharp edge 13 and this severs the rubber deposit at the sharp edge on a smooth line leaving the integral reinforcing head 16 around the opening of the shoe made by the severing of the deposit. The film is then leached in water, dried and vulcanized. Natural rubber films made by dipping twice in the latex with a coagulant dip in between have also been severed with gasoline. Similar one and two latex dip rubber films from so-called cold GR-S latex (emulsion copolymerizate of 71 parts of butadiene and 29 parts of styrene at 41 F.) have also been successfully severed with gasoline. With films from synthetic rubber latices that are highly resistant to aliphatic hydrocarbons, the aromatic hydrocarbon rubber swelling agents, such as toluene, may sever the rubber film more readily than aliphatic hydrocarbon rubber swelling agents.

The latex may be a natural rubber latex, or a synthetic rubber latex, or a mixture of any of them. The synthetic rubber latex may be an aqueous emulsion polymerizate of one or a mixture of butadienes-1,3, e. g., butadiene-1,3, 2-methyl-butadiene-1,3, 2-chloro-butadiene-l,3, 2,3-dimethylbutadiene-l,3, piperylene, or an aqueous emulsion polymerizate of a mixture of one or more such butadienes-1,3, with one or more other polymerizable compounds which are capable of forming rubbery copolymers with butadienes-1,3, e. g., up to 70% by weight of such mixture of one or more mono-ethylenically unsaturated compounds which contain a CH2=C group where at least one of the disconnected valences is attached to an electro-negative group, that is, a group which substantially increases the electrical dissymmetry or polar character of the molecule, such copolymerizable monoethylenically unsaturated compounds being exemplified by aryl olefines, such as styrene and vinyl naphthylene; the alpha methylene carboxylic acids and their esters, nitriles and amides, such as acrylic acid, methyl acrylate, methyl methacrylate, acrylonitrile, methacrylonitrile, methacrylamide; methyl vinyl ether; methyl vinyl ketone; vinylidene chloride.

In view of the many changes and modifications that may be made without departing from the principles underlying the invention, reference should be made to the appended claims for an understanding of the scope of the protection afforded the invention.

Having thus described my invention, what I claim and desire to protect by Letters Patent is:

1. The method of severing a rubber film deposited from latex on a sharp edge of a deposition form, said film being under tension over said sharp edge, which comprises applying to the rubber deposit on the sharp edge a rubber swelling agent, whereby the film is severed at the sharp edge.

2. The method of severing a rubber film deposited from latex on the sharp edge of a metal rib protruding from the surface of a deposition form, said film being under tension over said sharp edge, which comprises applying to the rubber deposit on the sharp edge a rubber swelling agent, the combined sulfur content of the film at the time of application of the swelling agent having not over 0.5% by weight of the rubber, whereby the film is severed at the sharp edge.

3. The method of severing a rubber film deposited from latex on a sharp edge of a deposition form and having less than 20% by weight moisture content, said film being under tension over said sharp edge, which comprises applying to the rubber deposit on the sharp edge a rubber swelling agent, whereby the film is severed at the sharp edge.

4. The method of severing a rubber film deposited from latex on the sharp edge of a metal rib protruding from the surface of a deposition form and having less than 20% by weight moisture content, said film being under tension over said sharp edge, which comprises applying to the rubber deposit on the sharp edge a rubber swelling agent, whereby the film is severed at the sharp edge.

5 The method of severing a rubber film deposited from latex on a sharp edge of a deposition form, said film being under tension over said sharp edge, which comprises applying gasoline to the rubber deposit on the sharp edge, the combined sulfur content of the film at the time of application of the swelling agent having not over 0.5 by weight of the rubber, whereby the film is severed at the sharp edge.

6. The method of severing a rubber film deposited from latex on the sharp edge of a metal rib protruding from the surface of a deposition form, said film being under tension over said sharp edge, which comprises applying gasoline to the rubber deposit on the sharp edge, whereby the film is severed at the sharp edge.

7. The method of severing a rubber film deposited from latex on a sharp edge of a deposition form and having less than 20% by weight moisture content, said film being under tension over said sharp edge, which comprises applying gasoline to the rubber deposit on the sharp edge, whereby the film is severed at the sharp edge.

8. The method of severing a rubber film deposited from latex on the sharp edge of a metal rib protruding from the surface of a deposition form and having less than 20% by weight moisture content, said film being under tension over said sharp edge, which comprises applying gasoline to the rubber deposit on the sharp edge, the combined sulfur content of the film at the time of application of the swelling agent having not over 0.5% by weight of the rubber, whereby the film is severed at the sharp edge.

References Cited in the file of this patent UNITED STATES PATENTS 1,670,598 Sutton May 22, 1928 1,951,402 Gammeter Mar. 20, 1934 2,095,119 Beal Oct. 5, 1937 2,397,340 Dable Mar. 26, 1946 

1. THE METHOD OF SEVERING A RUBBER FILM DEPOSITED FROM LATEX ON A SHARP EDGE OF A DEPOSITION FORM, SAID FILM BEING UNDER TENSION OVER SAID SHARP EDGE, WHICH COMPRISES APPLYING TO THE RUBBER DEPOSIT ON THE SHARP EDGE A RUBBER SWELLING AGENT, WHEREBY THE FILM IS SERVED AT THE SHARP EDGE. 